This invention relates to an inertia switch.
Supplemental inflatable restraint devices that are used in automobiles are activated by inertia switches. These switches sense predetermined deceleration characteristics and provide switch closure signals to the devices when such predetermined characteristics are sensed. The predetermined deceleration characteristic that creates switch closure is a function of both the magnitude of deceleration and its duration. The ability of a switch to sense a predetermined deceleration characteristic is determined by the switch design. In order to embody this design in production switches, manufacturing tolerances must be closely controlled.
One known type of inertia switch that is used with supplemental inflatable restraint devices comprises a sphere that travels within a tube. The predetermined deceleration characteristic that will activate the switch is a function of several parameters. One of these parameters is the closeness of the fit of the sphere within the tube. Controlling the accuracy of this fit in production switches is a significant portion of the switch cost.
The present invention relates to an inertia switch which does not utilize the tube and sphere construction and for that reason offers the potential for reducing costs associated with the production of inertia switches for supplemental inflatable restraints while still attaining a specified degree of accuracy in such switches.
Briefly, a switch embodying principles of the invention comprises a casing containing a diaphragm that divides the casing into two chambers. The diaphragm can move axially within the casing. An electrical contact is carried by the face of the diaphragm that bounds one chamber. Terminals are disposed in that chamber in the path of travel of the electrical contact as the diaphragm moves toward that chamber. The face of the diaphragm that is toward the other chamber carries a mass since the electrical contact may be insufficient by itself to provide enough mass for the diaphragm. The diaphragm is constructed such that the electrical contact is biased out of contact with the terminals, and this represents the off condition of the switch. In response to an axial force urging the mass, diaphragm, and electrical contact toward the terminals, the electrical contact will be forced to make contact with the terminals provided that a predetermined deceleration characteristic is exceeded. This represents the closed condition of the switch, whereby the switch provides a signal to an associated supplemental inflatable restraint system.
The predetermined deceleration characteristic that causes switch closure is a function not just of the diaphragm and the mass that it carries, but also of a control orifice. The control orifice is provided in an orifice structure passing through the electrical contact, the diaphragm, and the mass, and serving to communicate each chamber to the other. The casing is constructed and arranged such that air must be forced through the control orifice as the diaphragm, the mass, and the electrical contact move toward the terminals, and accordingly, the control orifice performs a timing function that forms a part of the predetermined deceleration characteristic to which the switch is responsive. Stated another way, the requirement that air be forced through the control orifice imparts a certain dampening to the diaphragm travel. In the disclosed embodiment of the invention the control orifice is in the electrical contact. The orifice can be formed quite accurately in the electrical contact by known methods, and in this way the timing function can be economically incorporated in production switches with the required degree of accuracy.
The foregoing features, advantages, and benefits of the invention, along with others, will be seen in the ensuing description, and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.